In the field of automotive transmissions, there are known mechanical automatic transmissions designed such that actuators perform gear operations (gear selection and shift) and clutch operations, instead of a driver manually doing these as in manual transmissions, thereby accomplishing automatic gear shifts. As one type of such mechanical automatic transmission, there is known a dual-clutch automatic transmission which has two clutches to transmit torque to gears and conducts gear shifts in the manner alternately transmitting drive torque to gears belonging to different groups.
In the dual-clutch automatic transmission, in order to reduce drive torque variations accompanying the clutch operations for gear shifts and reduce time taken for gear shifts, a process called “pre-shift” is performed. Specifically, the gear to be selected next is determined from vehicle traveling state and others and preselected while its associated clutch is disconnected, or on standby, and then, the gear shift is accomplished by engaging the standby clutch and disengaging the other clutch.
As exemplified by Japanese Patent Application Laid-open (Kokai) No. 2010-36781, there is known a dual-clutch automatic transmission for a hybrid vehicle having an internal combustion engine and an electric motor as power sources, comprising a first and a second transmission units each having an input shaft, the input shaft of the first transmission unit engaging with a rotor of the electric motor, wherein a smooth gear shift is conducted by bringing the rotating speed of the input shaft of the first transmission unit to a desired level matching the vehicle speed and a gear to be selected next, by means of the electric motor, while no gear is selected in the first transmission unit, thereby enabling a skip gear shift in the first transmission unit with the clutch associated with the first transmission unit being kept engaged.